Herein is described a genetic epidemiological study of the role of variation in lipoprotein phenotypes and lipid fractions in determining certain forms of atherosclerotic disease. This study will be based on 4,565 individuals in three different sets of pedigrees collected as part of the Rochester SCOR program in atherosclerosis (1971-1977). Pedigrees will be analyzed to provide insight into appropriate intervention strategies. In particular, we shall: l) determine the contribution of genetic and environmental variability to lipid variability within and among families; 2) test for heterogeneity of the genetic and environmental contributions to lipid variability among sets of families identified by probands with different lipid levels, quantitative lipoprotein phenotypes or atherosclerotic disease; 3) search for evidence of segregation at one or more loci with major effects on the lipid phenotype; 4) assess the relative risks of atherosclerotic disease in the adult relatives of different types of probands; and 5) relate sources (shared environment, shared polygenes and/or shared major loci) of familial aggregation of lipid phenotype to the risk of atherosclerotic disease.